4
Let me preface this by "I haven't actually tried this but..."
As long as you don't mind not also having a 'top posters' block the easiest way is to change the top poster block into a random user block.
You'll need to comment out a couple of lines in the 'b_system_topposters_show' function and then add a couple of new lines. In XOOPS versions 2.0.16-2.0.17.1 comment out lines 300-301 in ./modules/system/blocks/system_blocks.php so they look like this:
// $criteria->setOrder('DESC');
// $criteria->setSort('posts');
Then add the following 2 lines immediately after those two lines.
$criteria->add('user_avatar','blank.gif','<>')
$criteria->setOrder('RAND');
I believe that should do it...
